Since 1978, a longitudinal study investigating the effects of marihuana and cigarettes used during pregnancy has been underway. The overall purpose of this Ottawa Prenatal Prospective Study (OPPS) is to examine the effects of these drugs on pregnancy, the neonate and the child. The general objective of this competitive renewal is to determine whether particular developmental sequelae and behavioral difficulties observed in the newborn, infant, and young child that are statistically associated, in a differential fashion, with prenatal marihuana and cigarette exposure persist in the o 1/2 to 11 year 11 month old child and whether, by an in depth neurobehavioural assessment, a greater degree of specificity of dysfunction can be identified. Additionally, because of the longitudinal nature of this OPPS, the predictive validity of the infant and early childhood tests can be examined as can the continuity of effects over age. The neurobehavioural battery will focus upon those behaviors which we have identified to be vulnerable to the drugs in question. In Particular the assessment will include an examination of language and auditory processing, aspects of reading (including visual and auditory components), visual and non-visual perception, motor tasks, memory tasks, reasoning ability, intelligence, academic readiness, impulsivity sustained attention, psychological status and behavior (as assessed by the parent, teacher and examiner). Material variables (e.g. health, nutrition, parity, education, age, other drugs, intelligence, personality) and postnatal, environmental variables (e.g. home environment, second hand smoke [using urine analysis and questionnaires], and schooling experience) will be included in multivariate statistical analysis. The OPPS is the only work to have published data on marihuana users' offspring beyond a very early childhood and is the most comprehensive longitudinal work examining school age children of cigarette smokers. The testing of children at approximately 10 years of age is particularly critical as the identification of subtle learning difficulties is most likely to manifest themselves when complex behaviors requiring focused attention and cognitive skills, normally present at this stage of development, can be examined in depth.